The Institute of Electrical and Electronic Engineers (IEEE) 802.11 standards address systems in which a number of stations (STAs) compete to conduct communications via the resources of an access point (AP). In this context, the IEEE 802.11 standards specify a medium access control sub-layer (a “MAC”) that is a carrier sense multiple access with collision avoidance (CSMA/CA) based medium access scheme; when the number of STAs contending for the medium is very large, there will be a high probability of collisions and the spectrum is wasted by the failed transmissions. The network throughput and packet transfer delay are degraded dramatically.
There are some techniques that can potentially solve this problem. Some of them are based on centrally-scheduled medium access; some techniques adapt the back-off window to match the number of STAs, which then reduces the probability of two STAs throwing the same random back-off value; other techniques are based on grouping STAs and only allowing STAs in the same group to contend for the medium. However, for these techniques to work, the AP needs to know how many STAs are in the network, and this information is not available until STAs finish their initial association.
When a large number of STAs is trying to associate with the AP simultaneously (with a short period of time of arrival difference, e.g. after a wide-area power cut), there is increased probability that the STAs will collide with each other and the medium could be congested. If the AP tunes the parameters, such as back-off window size or number of groups, assuming a large number of STAs, the network throughput can also be compromised due to waste of spectrum resource in waiting for non-existent STAs contending for medium. Therefore, there is a need for a scheme to manage the contentions from a potentially large number of STAs and a need for a scheme can to manage contentions before, as well as after, association.